A major problem encountered in the metal fabricating industry is the need to machine holes, slots, grooves and the like in predetermined positions in a workpiece and to perform the machining with a high degree of precision and accuracy. Machine tools (such as a drill press or milling machine) used for machining generally include a chuck for holding a tool bit or cutter and a workpiece holder for holding a workpiece. The workpiece holder may be a vise or a jig and is usually slidably mounted on the machine tool and its position may be adjusted by handcranks with graduated dials. A problem is encountered due to the fact that it is difficult to precisely position the workpiece with respect to the chuck. The relative positioning of a tool bit held by the chuck and the workpiece is crucial to attaining accuracy and precision in performing a machining operation. For example, if a hole is to be bored in a preselected position in a workpiece, the workpiece must be precisely aligned with and positioned with respect to a tool bit which is to machine the bore.
Various types of electrical and non-electrical devices have been used in the past in order to attempt to correctly align the chuck of a machine tool with a workpiece. A major problem with most prior devices is that in order to make a center location or edge measurement, it was required that the chuck of the machine tool be rotated. For example, a non-electric center locator used in the past had a shank with a spring loaded contact sensor mounted thereon. Such a prior center locator would be mounted in the chuck of a machine tool with the spring loaded contact mounted off axis from the shank. As the chuck was rotated, the workpiece would be manually moved to the contact until the contact is pushed into axial alignment with the shaft. Then the operator continues to move the workpiece a small distance until the contact pops out of axial alignment with the shaft so that the operator can visually notice the point of axial alignment. Based on the position noted by the operator, approximate alignment between a tool bit and the workpiece could be computed.
A prior type of electrical center locator included the use of a pivoting arm mounted on a shank and connected to an electric light. The pivoting arm would be manually pivoted into an off axis position from the shank and the shank would be mounted in the chuck of a machine tool. The chuck of the machine tool would be rotated and the workpiece would be moved into contact with the pivoting arm. As the workpiece was moved, the pivoting arm would be displaced until the pivoting arm was in axial alignment with the shank. A circuit would be used to control the light so that the light would turn off when the pivoting arm was in axial alignment with the shank.
A problem with prior center locator devices and methods is that accuracy and precision of such prior devices and methods depended upon precise tolerances which were difficult to achieve in their manufacture and operation. Another problem with the prior center locator methods is that undue amounts of time and operator's skill were required in order to obtain acceptable results. A further problem with the prior devices and methods is that rotation of the machine tool chuck was required in order to perform the measurements. A further problem with the prior devices and methods is that the probes provided lacked versatility to adapt to unusual workpiece shapes, and the probes used were unduly expensive.